Problem: Solve for $k$, $ \dfrac{5k - 9}{5k + 4} = 9$
Answer: Multiply both sides of the equation by $5k + 4$ $ 5k - 9 = 9(5k + 4) $ $5k - 9 = 45k + 36$ $-9 = 40k + 36$ $-45 = 40k$ $40k = -45$ $k = -\dfrac{45}{40}$ Simplify. $k = -\dfrac{9}{8}$